Refilling of Colorado River lakes all but unthinkable, experts say

Lakes Powell and Mead, the depleted symbols of the Colorado River’s water crisis, are unlikely to ever fill again, several water experts say.

This year’s extremely heavy snowpack in the river’s Upper Basin states will produce the river’s second highest annual flow of the 21st century, federal forecasts show. The river is expected to bring 18.6 million acre-feet of water to Lee’s Ferry, lying between Glen Canyon Dam and the Grand Canyon in northern Arizona, the U.S. Bureau of Reclamation predicts.

The flow is likely to be 80% to 140% greater than the river has carried in any of the previous three years, federal records show.

But given the reservoirs’ precarious conditions, with both carrying 25% to 30% of their capacity today, it would take another four or five consecutive years of high flows like this one to fill Powell and Mead again, said Brad Udall, a Colorado State University climate scientist, and Eric Kuhn, a water researcher and former general manager of the Colorado River Water Conservation District in Glenwood Springs, Colo.

That’s highly unlikely or impossible, with the river carrying about 20% less water, on average, each year than it did during the 20th century, Udall and Kuhn said.

“We’re in a century with extreme climate change that is reducing flows in most years due to human-caused increases in heat,” Udall said.

Officials in Reclamation’s Upper and Lower Basin offices didn’t respond to questions from the Star about whether they agree with Udall and Kuhn’s gloomy outlook for the lakes.

But at a federally sponsored webinar held Tuesday, May 9, Paul Miller, a hydrologist for the federal Colorado River Basin Forecast Center, said he believes it could take even six to eight years like this one to refill all the reservoirs in the river’s Upper Colorado River Basin, plus Lake Mead in the Lower Colorado River Basin — “which probably isn’t very likely.”

Miller noted that Jennifer Pitt, a longtime Colorado River activist for the National Audubon Society, has recently concluded that “if we had normal snowpack conditions for three straight years and also zero water use, we’d refill the majority of the Upper Colorado Basin reservoirs.” Miller based his six- to eight-year estimate on Pitt’s logic, but “knowing we are not ever going to not use water.”

The webinar was sponsored by the National integrated Drought Information System, a branch of the National Oceanic and Atmospherics Administration. A second speaker, Andrew Hoell, a research meteorologist for NOAA’s physical sciences laboratory, said Miller’s “back of the envelope calculations” are realistic.

While the lack of soil moisture due to hot, dry springs and summers has repeatedly held down runoff into Lake Powell in recent years, this year, “Things are copacetic now. They’re great,” Hoell said.

“The snow is going to run off and replenish the soil moisture. But it will take longer for reservoirs to recharge. They need the sustained behavior for many years. We need to go into a wet regime to refill those reservoirs.”

Cutting water use

The reservoirs are in bad enough shape that the bureau is studying two alternatives for curbing consumption of river water by the Lower Basin states of Arizona, California and Nevada by 2 million to 4 million acre-feet a year. Such a cut, starting next year, would be equivalent to up to nearly 30% of current levels of use.

Such reductions are needed to insure the lakes don’t fall so low that their dams can no longer generate electricity, let alone to “dead pool,” in which no water could be extracted from them, bureau officials have said.

The bureau is expected to announce a final decision on cuts by August. Arizona and the six other river basin states’ water officials are trying to negotiate their own agreement to avoid taking more draconian, federally imposed reductions.

But the reservoirs’ situation may not be hopeless even if they don’t refill. Even in today’s drier climate, it’s still possible the river could get enough consecutive years of better than average flows — as occurred during the late 1990s — to give the Colorado a breather and stave off drastic cuts for awhile, Kuhn and Udall said. While such a string of wet weather years wouldn’t fill the lakes, they would lift their levels to at least half full.

The river carried 21.6, 16.6 and 15.8 million acre-feet a year, respectively, from 1997 through 1999. All three flows were well above the Colorado’s average, annual natural flow of 15 million acre-feet during the 1900s — an average that has fallen sharply since then. Since 2000, the Colorado has never had even two consecutive years of above-normal flows, federal records show.

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“Maybe that would not completely fill the reservoirs, but it would certainly give us plenty of maneuvering room,” Kuhn said.

While agreeing with Kuhn, Udall added, “I’ve always said that we could get a string of wet years but that the overall aridification trend in the long run means it will get hotter and drier over time. Not every year will be hotter and not every year will be drier, but that’s our future.”

But even if the river had three wet years combined with 4 million acre-feet annually in water use curbs, that would still not refill the reservoirs entirely, he said.

“More importantly, I cannot envision any set of circumstances ever where once these reservoirs went to half full that anyone would want to endure the pain of 4 million acre-feet a year cuts,” Udall said. “Historically, this whole system has been designed to push out as much water as possible every year.”

Pattern: Dry years after wet ones

The last time the Colorado had four lush years in a row was also the last time both reservoirs filled: 1983 through 1986.

In those years, the river regularly experienced flooding, sometimes very serious. Between 21 million to 24 million acre-feet a year poured through Lee’s Ferry, a natural corridor between Utah and Arizona where the federal government measures river flows.

That’s more water than all the Colorado’s 13 major reservoirs are storing today. The last time Powell and Mead came even close to filling was in 1999.

The mid-’80s were part of an unusually wet era on the river that stretched from the late 1970s to the late 1990s. Since then, the Colorado River Basin, along with the entire Southwest, has suffered through its worst drought in 1,200 years.

“Considering the magnitude of the 20th century flows . . . the unprecedented warmth since the 1970s, the repeated low flows since 2000, and additional certain warmth going forward due to continuing massive greenhouse gas emissions, the only possible conclusion is that a system refill is exceedingly unlikely,” said Udall. Son of the late, longtime U.S. Rep. Mo Udall of Tucson, he has been at the forefront of scientists warning about risks to the river from climate change since the early 2000s.

Lake Powell in early May stood 25% full, at about 3,525 feet. At the same time, Mead stood at 29% full, at 1,049 feet elevation.

Udall noted that over the past decade or so, a pattern has developed in which very wet years in 2011, 2017 and 2019 were followed by one or more very dry years.

In fact, 2018 had the lowest precipitation across the river’s Upper Basin of any year since 1895, when records started being kept. The 23-year period ending in 2022 also had the lowest 23-year average precipitation on record, he said.

“Yes, climate change can provide very wet years like this year — and we should expect these years — but they will not make up for the more frequent hot and dry intervening years,” Udall said.

Kuhn noted that many forecasters are already predicting that the upcoming winter of 2023-24 will be an El Niño winter, in which the Southwest gets unusually heavy rains and in which the Colorado’s Upper Basin can but doesn’t always get unusually heavy winter precipitation. The Upper Basin states include Colorado, New Mexico, Utah and Wyoming.

“If 2023-24 is indeed a strong El Niño, I would not rule out a three-year wet period similar to 1997 ,’98, and ‘99,” he said. “Of course, there is no guarantee that we’ll actually have a strong El Niño or that if we have one, it will be a wet year.”

Photos: The receding waters of Lake Powell, Glen Canyon National Recreation Area